Experts attending a major agricultural conference in Sydney say big changes will need to be made to farming practices to help offset global warming.

Agricultural scientists from more than 60 countries have gathered in Sydney to discuss ways to improve the efficiency of farming.

They say global warming is expected to create drought hotspots, while more floods would damage agricultural land in Asia.

Professor Jean-Francois Soussana, who shared a Nobel Peace Prize for his work on climate change in 2007, says parts of Australia and Africa are likely to become drought 'hotspots'.

"In some places we get presumably a reduction in rainfall that would cause an increase in drought, and this would strongly affect the ecosystems and the agriculture," he said.

"There are many uncertainties still on when exactly and where those droughts would occur, but the understanding is that you would have some drying hotspots in some parts of the world, for instance, in Southern Africa, but also in parts of Australia.

"We can see that this would likely cause some damage to livestock and especially to pastoralists."

He says across the Asia-Pacific region, the effects on agriculture will vary.

"Some of the major risks we are aware of for Asia concerns the delta areas, because they will get a lot more flooding, and this would induce large risks for some of the crops," he said.

"There are some more specific studies for rice, that find rice would be at risk from warming at the flowering stage. "

Professor Soussana is one of more than a thousand delegates attending the International Grassland Congress in Sydney, a meeting that only takes place every four years.

Delegates have heard that reducing the carbon footprint of global agriculture is just one challenge.

Dr Jimmy Smith, head of the International Livestock Research Institute, says the more immediate question is how to feed the world's booming population.

"Estimates show that between now and 2050 the world will need to produce about one billion tonnes more cereal, and about half of that would be used for livestock feed and the other half for human consumption," he said.

"We would need about a billion tonnes of dairy commodities a year by 2050, and we will need about 450 million tonnes meat annually."

He says the jury's out on whether producing that much food is even possible.

"We are not so sure where we would find the technologies to produce those levels of meat and milk and cereals on a fixed land base, which some say is already reaching its ecological limits, but that's what our research is about," he said.

"Much of that increase would have to come from increases in productivity, because the suitable land for agriculture has largely been used."

Helping farmers get more bang for their buck is seen as the best way to address food security and to help reduce the huge contribution that agriculture makes to global carbon emissions.

Dr Smith says the focus must now shift from large-scale agriculture to the small-scale farmers who dominate in South Asia and sub-Saharan Africa.

"Certainly smallholders of the world who have largely been subsistence farmers, we need to connect more of them to markets," he said.

"And by doing so, we allow them to contribute more effectively to aggregate food supply, but by connecting them to markets, we also allow them to earn more income, because even though there is so much livestock products produced in the world, only about ten per cent of it is traded.

"So trade in the livestock commodities is relatively low at the moment, it will increase in the future but it's still relatively low, so local markets matter."